Existing HyperText Transfer Protocol (HTTP) caches treat segmented video in a manner similar to HTTP web content. Typical algorithms that are used by the cache manager for eviction of segments from the cache memory or for pre-fetching segments from the content server for storage in the cache memory are based on least-recently-used (LRU) or least-frequently-used (LFU) mechanisms.
The main drawback of LRU or LFU based cache management when applied to segmented multimedia that is available in multiple qualities, resides in the fact that temporal dependencies and quality-based dependencies between the segments are not exploited, as a result of which the cache hit rate is not optimized.
European Patent Application EP 0 702 491 entitled “Video Optimized Media Streamer with Cache Management” describes an improved video cache that takes into account temporal dependencies between video segments for scheduling transfers between mass storage and a cache buffer. Thus, the nature of video streams with temporally ordered segments is used in pre-fetching video segments in order to improve the cache efficiency.
EP 0 702 491 however does not consider the availability of multiple qualities of a single video item and the possibility for the client to dynamically switch between these qualities depending for instance on the availability of resources. As a result, the cache algorithm disclosed in EP 0 702 491 does not optimize the cache hit rate when multimedia items can be requested in different qualities and the requested quality may adaptively change during consumption of the multimedia like for instance with HTTP Adaptive Streaming (HAS) of video.
In particular for intermediate cache nodes with limited capacity, e.g. HTTP caches in access nodes, improvements in the caching algorithms may result in significant increase of the cache hit rates and consequently of the benefit/cost ratio when deploying such caches.
It is therefore an objective of the present invention to disclose a cache manager and a corresponding cache management method that resolves the above mentioned shortcomings of existing solutions. More particularly, it is an objective to disclose a cache manager and corresponding cache management method with improved cache hit rate for segmented multimedia available in multiple qualities.